HAVANA—All the ingredients for decadence were there: scantily clad beauties, 90-degree temperatures, and an endless supply of cheap mojitos, the Cuban rum drink flavored with mint and lime.

But no impressive tan lines loomed in the future for these nine Amherst College students. Instead, their spring break last month featured 8 a.m. wake-up calls, hostel-style bunk beds, and a week of meetings with supporters of Cuba’s Communist Party.

As their friends slept off hangovers or soaked in the Caribbean, the Amherst group paid $1,400 per person to talk in humid conference rooms with Marxist students and economists and leaf through books like ‘‘The Truth About the United States.’‘

‘‘You’re late,’’ Nicholas Wexler, a 21-year-old history major from Newton, was told as he and his friends crept in one morning, bleary-eyed after a long night on the town.

Although the United States broke diplomatic ties with Cuba four decades ago and now bans most travel and trade to the country, ‘‘alternative spring breaks’’ and educational tours have mushroomed here in recent years under Clinton-era travel laws that sought to democratize the socialist island through social contact. But late last month Bush administration officials proposed sweeping new restrictions on such trips to Cuba.

‘‘Tourist travel and open-ended `solidary visits’ to Cuba do not reinforce US goals,’’ said Charles Barclay, a US State Department Spokesman. ‘‘The latest move is to tighten up procedures, so that people demonstrate that they are going down there for the kind of `focused people-to-people’ contact that we want to promote.’‘

The move is a setback for Cuba, which is eager to showcase the bright side of the Marxist island to idealistic young Americans and build the billion-dollar tourist industry that has been a lifeline since the fall of the Soviet Union.

It is also a blow for US students, who swarmed into Havana by the hundreds in recent weeks on separate spring break trips.

They came from Amherst, Harvard, Princeton, Cornell, and a host of other US colleges.

‘‘It’s not about being in 90-degree weather,’’ said Nelly Almeida, 18, who regretfully returned to Amherst College without a tan. ‘‘I wanted to see for myself what communism was like.’‘

It wasn’t most people’s vision of an ideal vacation: a $100 shopping limit, free time restricted by law, more than 14 hours of mandatory discussion and reflection, and toilets that can’t flush toilet paper. But they worked hard to get there, selling raffle tickets and doughnuts and braving the barbs of family and friends who fretted about them turning ‘‘commy.’’ Even at Amherst College, where the president’s wife once spent a brief stint in a Cuban revolutionary brigade, they found themselves explaining why they opted to spend their spring break conversing about Castro.

‘‘A lot of people at Amherst think this is the most radical group of kids,’’ said Wexler. ‘‘A lot of people assume it’s just liberal brainwashing.’‘

The label doesn’t apply. Wexler says he is a ‘‘commited skeptic’’ about both Cuba and the United States. Ashley Bates, a senior majoring in political science, has a fondness for the conservative writer Ayn Rand and a deep reverence for theories of capitalism. And Almeida, a sophomore originally from Ecuador, wants to run an afterschool program, but after she gets rich.

All three completed a class on Cuban politics that taught them to be wary of Cuban propaganda. All three were enthralled by Cuba when they arrived.

Bused around on a tight schedule by Witness for Peace, a US-based human rights group that opposes the trade and travel embargo on Cuba, the students’ schedule was tight: A lecture on the sugar-cane sector; a chance to ask a Cuban government official about the recent arrests of so-called counterrevolutionaries; a night of mandatory salsa lessons.

At first, Cuba showed its charms. At the Museum of the Revolution gift shop, photos of Ernesto ‘‘Che’’ Guevara prompted the sophomores to swoon. Then came a visit to a clinic, with socialized health care nicely showcased when one sick member of the delegation received a shot in the buttocks, completely free of charge.

And most impressive of all was the school, where Cuban youngsters sang patriotic songs and invited the Amherst group to participate. After a brief huddle to pick an appropriate song, ‘‘The Star-Spangled Banner’’ was ruled out, and the Americans settled on ‘‘The Hokey-Pokey.’‘

‘‘I thought that was so pathetic,’’ Almeida said later. ‘‘They sang this heart-filled song to us, their faces were just filled with passion, and all we could sing was `The Hokey-Pokey.’ ‘’

By the middle of the week—after three disco nights, two lectures from Protestant pastors, and long reflection sessions—people-to-people contact began to show Cuba’s other face.

At a disco, Travis Bristol, a senior, chatted with an 18-year-old prostitute who told him that government rations can’t get her family through the month.

Bates met a Cuban man who was dabbling in illegal self-employment, because he couldn’t stand having the government looking over his shoulder, telling him how to do his job.

‘‘I think it’s great that you’re trying to make it on your own,’’ she told him. His eyes lit up, and the two talked for almost an hour.

It’s these kinds of interactions that US government officials had in mind when they loosened restrictions on some structured educational travel in 1992 and again in 1999.

‘‘Hearing Americans describe how they go about their daily lives is a radical enough idea in this society to be of tremendous importance,’’ said one American diplomat in Havana.

But on March 25, the US government sought to eliminate most travel licenses for ‘‘people-to-people’’ educational exchanges, on which tens of thousands of Americans have traveled to Cuba.

‘‘There are too many individuals and groups that are going down there for the sake of tourism,’’ Barclay said.

It is unclear how the new policy will effect Witness for Peace, which operates on a religous license, or other groups that hold licenses for humanitarian or for-credit academic travel. What is clear is that alternative spring breaks to Cuba will be far harder to take next year, bad news for Marisa Parham, the Amherst assistant professor of English who helped organize and chaperon the college trip.

‘‘We’re being used by both sides, when the purpose of the trip is to get you to think and come to your own conclusions,’’ she said.

On a Friday afternoon, two days before they flew back to their old life in capitalist America, the Amherst students piled into their bus and rode to the US Interest Section, which handles American affairs in Havana. Outside, Cubans have erected a statue of a revolutionary hero pointing in disgust.

The students, bubbling over with anger at the US government, sat down and peppered a State Department official with questions about why Cuba had been singled out for an embargo.

Her answer, ‘‘It’s a matter of national security,’’ left them looking skeptical.

But the toilet there, the first they had used all week that flushed paper, left an even deeper impression.

Deep into the night, they discussed the toilet’s healthy, American-style flush, as they changed into sandals and shorts for an evening in Havana. Then they set off toward the crowds of Cuban revelers, searching for people-to-people contact.